a. Field of the Invention
The present invention relates to a catheter employed for diagnostic and/or therapeutic procedures in medicine, more specifically in minimally invasive cardiac electrophysiology studies and/or cardiac ablation procedures.
b. Description of the Prior Art
The primary device for an intra-cardiac electrophysiology study is a catheter with conductive electrodes at its distal portion [U.S. Pat. Nos. 5,156,151, 5,279,299, 5,415,633, 5,454,370, 5,465,717]. The distal portion of the catheter, where the electrodes are located, is commonly placed transvenously into the heart to monitor and/or record the intra-cardiac electrical signals during electrophysiology studies, or during intra-cardiac mapping. The function of these electrodes on the catheter is to conduct cardiac electrical signals to appropriate monitoring and recording devices.
During the diagnostic procedures, the catheter is also used as a medium to deliver low energy electrical pulses from a cardiac stimulator to the heart in order to evaluate the heart's response to the cardiac stimulator signals.
During therapeutic (cardiac ablation) procedures, electrical energy in the form of radio-frequency, microwave or high-voltage pulses is delivered from an appropriate energy source to the heart commonly via the catheter's distal electrode. The intent of this energy delivery is to destroy the site of the cardiac tissue that causes abnormality (arrhythmia) to the normal rhythm of the heart.
During such a minimally invasive cardiac ablation procedure the distal portion of a catheter, which usually comprises a plurality of spaced annular cylindrical electrodes and a distal electrode, is transvenously placed into the heart. The proximal end of the catheter, remote from the electrodes, has electrical leads which are connected to an appropriate recording and/or monitoring device. The intra-cardiac electrical signals can then be monitored and recorded.
A surface electrocardiogram, obtained from patient's skin, is concurrently compared with the intra-cardiac electrical signals. Typically, when a known catheter is employed for ablation procedures, an electrically conductive self adhesive skin patch is also placed on the patient's body. An electrical lead from this patch is connected to an electrical energy source. As the abnormal site of the cardiac tissue is detected with the catheter's distal electrode, its corresponding electrical lead is switched from the monitoring/recording device to the electrical energy source for ablation. At this time, electrical energy can be delivered to the heart from the catheter tip that is in contact with abnormal heart tissue. The self adhesive patch on the patient's body is the return path of the electrical energy to the energy source. This known ablation procedure, using a self-adhesive patch as the return path of electrical energy to the energy source, may result in a significant level of electrical “noise” that is generated by the energy source during the energy delivery period. This “noise” superimposes itself to both surface electrocardiograms and intra-cardiac signals obtained from the catheter. Cardiac signals contaminated with such “noise” have been found difficult to monitor during energy delivery period.
Intra-cardiac signals are commonly acquired for electrophysiology studies via a selected pair of a catheter's electrodes. The catheter is said to be used as a bi-polar probe when a cardiac signal is obtained between any pair of its electrodes. In some electrophysiology studies or cardiac mapping, however, the catheter is used as a uni-polar probe. When catheters of the prior art have been employed as a uni-polar probe, an additional reference electrode, that is not a part of the inserted catheter, is needed to complete the electrical circuit path. In such an arrangement, a second catheter is transvenously placed into the heart and this second catheter electrode functions as the reference electrode. U.S. Pat. No. 4,920,980 describes uni-polar and bio-polar application of cardiac catheters.
Currently most widely used and commercially available cardiac diagnostic and ablation catheters are sold for “one-time-use-only”, and the entire catheter is discarded after a single use. Catheters of this type are relatively expensive. The catheter price and the convention of its “one-time-use-only” have an impact on the overall cost of cardiac electrophysiology and ablation procedures.
Typically, known catheters have a generally cylindrical electrically non-conductive body which has a plurality of spaced annular surface electrodes on the distal end with a hemispherically-shaped tip electrode. Each electrode has a relatively fine electrically conductive wire attached thereto and embedded in the catheter's main body (tube) and extending from the distal end to the proximal end (catheter handle) where the electrical connectors such as plugs or jacks are provided to be plugged into a corresponding sockets provided in recording and monitoring devices.
Typically, the main body of these catheters comprises a flexible tube constructed from polyurethane, nylon or some other electrically non-conductive flexible material with braided steel wires or other non metallic fibers in its wall as re-enforcing elements. An early example of such construction is that shown and described in U.S. Pat. No. 3,416,531 issued to M. L. Edwards. Catheters of this type are available in two general categories: a) those having a non-deflectable distal portion, an example of which is shown and described in U.S. Pat. No. 3,190,286 issued to R. W. Stokes, and b) those having a deflectable distal portion, as for example the catheter shown and described in U.S. Pat. No. 3,605,725 issued to I. E. Bentov. The distal portion of deflectable type catheters is typically made from non-braided flexible tube. This portion can be deformed into a variety of curved configurations with different radii of curvature by means of user input to a manual actuator on the catheter handle. The actuator is commonly internally linked to the catheter distal portion or the tip electrode by at least one steel tension or pull wire.
The proximal end of the tension or pull wire(s) is connected to a tensioning or puller mechanism in the handle. The distal end of the tension or pull wire(s) is fixed to the catheter distal electrode or anchored to a point on the catheter distal portion.
Catheters of this type also commonly comprise a flexible guide tube within the main body (tube) for bearing, in longitudinal or axial direction, the thrust or compression reaction of the flexible pull wire(s). An example of this latter type of configuration is shown and described in U.S. Pat. No. 3,906,938 issued to J. J. Fleischhacher and U.S. Pat. No. 3,521,620 issued to W. A. Cook. In the catheters of the prior art, such as those described in the aforesaid Cook and Fleischhacher patents, the inner flexible guide tube is formed by winding a tight coil of spring wire with the adjacent turns in contacting or closed relationship so that the inner guide tube will not compress longitudinally, but is freely flexible in bending. The tension wire(s) slides freely through this guide or coil spring type inner tube. The proximal end of the inner guide tube, in the aforesaid type catheters, is fixed to the catheter handle. The distal end of the inner guide tube is disposed in the distal portion of the catheter tubular main body. In one known catheter construction, one end of a bendable compression strut is seated on the distal end of the inner guide tube; and, the distal end of the pull wire(s) is fixed to the distal end of a bendable strut. Catheters employing such a strut are shown and described in the aforementioned Cook and Fleischhacher patents. See also U.S. Pat. No. 5,108,368 issued to Hammerslag for a catheter with a strut. In such known catheters, as tension is applied to the pull wire by the manual actuator on the catheter handle, the catheter distal portion assumes a curved configuration.
One of the distinctive parts of deflectable distal portion catheters is the pull wire mechanism that is commonly located in the proximal end (handle) of the catheter. This mechanism usually includes a manual actuator by which the catheter distal portion can be deflected. The primary difference among the designs of deflectable distal portion catheters is in the catheter handle, more specifically, the tension or pull wire mechanism. This mechanism transmits the manual force applied to the actuator on the handle to the catheter distal portion via the pull wire(s), for formation of a desirable radius of curvature at the distal portion of the catheter. A catheter employing a partially rotating “wheel” or “cam” mechanism for pull wire(s) is disclosed in U.S. Pat. No. 5,273,535 issued to S. D. Edwards et al. A rectilinearly moving arrangement for the pull wire is disclosed in U.S. Pat. No. 4,960,134 issued to W. W. Webster, Jr. A shapeable or bendable catheter handle for curvature formation on the distal portion of the catheter is disclosed in U.S. Pat. No. 5,318,525 issued to Scott West et al. A rotating collar or thumb-wheel type actuator is disclosed in U.S. Pat. No. 3,416,531, issued to M. L. Edwards.
The primary desirable performance features of the deflectable distal portion catheters are:
Ease of operation: ergonomic design to provide for the best use of physician's hand anatomy for catheter handling and usage;
A relatively low force requirement on the manual actuator of the catheter handle for formation of curvature at the catheter distal portion;
A comfortable range of displacement of the manual actuator to provide for a full range of curvature formation at the distal portion of the catheter; and,
A simultaneous curvature formation and curvature retention at the distal portion of the catheter by a single action of the physician's finger(s).
The above desirable performance features for the catheters with deflectable distal portion have not been met by known commercially available catheters. The catheters of the prior art referenced in this document have not satisfied all of the desirable performance features mentioned above. For example, in the aforesaid U.S. Pat. No. 4,960,134, issued to Webster Jr., the sliding pull wire arrangement does not satisfy the low force requirement on the manual actuator of the catheter handle for formation of curvature at the catheter distal portion.
In the aforesaid U.S. Pat. No. 5,273,535, issued to Edward et al, a catheter is disclosed with two manual actuators on the catheter handle; one actuator is employed for formation of curvature at the distal portion of the catheter; and, the other actuator is used for retention of curvature or locking. This catheter requires two independent manual actions on both actuators in order to form and retain a desirable radius of curvature on the distal portion of the catheter. Therefore, the Catheter of U.S. Pat. No. 5,273,535 (Edwards et al) fails to satisfy a simultaneous curvature formation and curvature retention at the distal portion of the catheter by a single action of the operators hand.
Attempts have been made in the prior art catheters to provide a relatively laterally flexible distal portion for ease of its navigation through the vascular branches of the heart. In U.S. Pat. No. 5,203,772, issued to Gary R. Hammerslag et al, a steerable tip guide wire is disclosed for percutaneous transluminal insertion into the coronary vascular branches. The structure of the guide wire of the '772 Hammerslag et al, catheter comprises a spring coil wherein adjacent loops of the spring coil are “closed” or normally in contact with each other, except the loops that form the deflectable distal portion of the guide wire. The closed or contacting loops and the open or non-contacting loops of the guide wire of the '772 Hammerslag et al construction provide an axially relatively non-compressible structure in the region of the stacked loops, with a relatively laterally flexible distal portion formed in the region of the open loops.
U.S. Pat. No. 3,521,620 issued to William Cook discloses a similar guide wire structure having contacting and non-contacting portions with a deflectable tip for the same intended use as the aforementioned Hammerslag '772 guide wire.
The cardiac catheters of the prior art are not only expensive but are solely for “one-time-use-only”. The catheter price and the convention of “one-time-use-only” increases the overall cost of electrophysiology and ablation procedures.
Presently employed known methods of cardiac ablation procedure and presently employed known ablation catheters have the disadvantage of requiring an electrically conductive patch on the patient skin during the procedure. The function of this patch is to return the delivered electrical charge, from the catheter electrode inside the heart, to the ablation energy source.